ECHIUROIDEA HABITS 



443 



boscis the nature of the bottom ; when the animal had found 

 a convenient crevice, it fixed its proboscis in it by means of 

 the bifurcated end, and by its contraction drew the body up, and 

 entered the hole, proboscis first. It then turned round, and during 

 this operation doubtless the ventral hooks came into play ; and 

 then stretching out its proboscis, it began to explore the 

 neighbourhood. The proboscis is evidently very sensitive, and 

 in addition to being a locomotor organ, it is also used for the 

 prehension of food. If cut off near the mouth, the animal does 

 not long survive, but if a considerable portion is left the scar 

 heals, and the lost part is probably regenerated. In captivity 

 the animals frequently change their place of residence. 



Eisig some years ago described the great extensibility of the 

 proboscis of B. viridis when confined in the tanks of the Zoo- 

 logical Station at Naples. When contracted the proboscis was 

 but a few inches long, but at times it was extended till it reached 



the 



length 



of 



H 



metre, shining through the water as a 

 transparent green thread. The body of the Bonellia was 

 hidden under stones, but the proboscis could be seen seizing 

 between its two ends the bodies of certain Ascidians which 

 covered the inside of the tank, tearing them off the walls, and 

 conveying them to the mouth along its grooved ventral surface. 



The food of the Echiuroidea consists of organic matter, in 

 the main of animal nature, but the group differs from the 

 Sipunculoidea in not eating sand. 



Eietsch describes Thalassema neptuni as being more active in 

 its movements and less seden- 

 tary than B. minor. The 

 proboscis is still the chief 

 organ of locomotion, but the 

 trunk plays a greater part in 

 the movements of the animal 

 than it does in the last-named 

 species. Th. neptuni is found 

 in cavities of stones or in 

 the chambers worn out by 

 the Mollusc Gastrochaena ; 

 when withdrawn from its 

 house the body is found to 

 tenacious viscid mucus. 



Fig. 224. Thalassema neptuni Gaert. x 2. 



A, The animal lying on its ventral surface. 



B, Ventral view of the anterior end, show- 

 ing the grooved proboscis ending behind 

 in the mouth, and the ventral hooks. 



be covered by a thick layer of 



